A method for purifying 1,2,3,6-tetrahydrophthalimide

Abstract

This invention discloses a method for purifying 1,2,3,6-tetrahydrophthalimide, comprising the following steps: mixing a hydrogen bond acceptor and a hydrogen bond donor, heating and stirring until a clear, transparent liquid is obtained, yielding a deep eutectic solvent; adding crude 1,2,3,6-tetrahydrophthalimide to the solvent and heating to dissolve, cooling to room temperature, adding water and stirring to precipitate crystals; filtering and collecting the precipitated crystals, washing with water and drying to obtain a high-purity product, the filtrate of which can be used for the recovery of the deep eutectic solvent. This invention utilizes the selective solubility characteristics of the deep eutectic solvent, combined with water-induced crystallization, to achieve efficient separation and purification, with a product purity of over 98%. The solvent used is recyclable, and no volatile organic solvents are used throughout the process, making it environmentally friendly and cost-effective. It is suitable for the recovery and utilization of tetrahydroimide from industrial crystallization mother liquor and waste residue, exhibiting significant economic and social benefits.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a method for purifying 1,2,3,6-tetrahydrophthalimide. Background Technology

[0002] 1,2,3,6-Tetrahydrophthalimide (Tetrahydroimide for short) is an important intermediate in the synthesis of broad-spectrum protective organosulfur fungicides such as captan and difenoconazole, and has wide applications in the pesticide industry. The purity of this compound directly affects the quality and efficacy of subsequent pesticide products; therefore, developing efficient and environmentally friendly purification methods is of significant economic and social importance.

[0003] Currently, the industrial production of 1,2,3,6-tetrahydrophthalimide typically involves reacting 1,2,3,6-tetrahydrophthalic anhydride with an ammonia source, followed by ring closure and recrystallization at a lower temperature to obtain the product. However, the mother liquor produced in this process still contains 1-1.5 wt% of 1,2,3,6-tetrahydrophthalimide and other organic impurities, such as tetrahydrophthalic acid, tetrahydrophthalic anhydride, and incompletely ring-closed intermediates. Traditional processing methods often involve direct distillation or evaporation crystallization, but these methods have the following problems:

[0004] Resource waste: Although the filter residue obtained from distillation contains more than 40 wt% tetrahydroimine, it is often disposed of as hazardous waste, resulting in serious loss of effective ingredients.

[0005] Equipment issues: When performing triple-effect evaporation directly, organic impurities can easily cause blockage of the heating tubes, requiring frequent unblocking and cleaning, resulting in high equipment maintenance costs.

[0006] Insufficient purity: Conventional recrystallization or extraction methods are insufficient to completely separate tetrahydroimine from structurally similar impurities, resulting in product purity often below 95%, which cannot meet the requirements for high-end pesticide synthesis.

[0007] Environmental burden: Existing methods mostly use volatile organic solvents (such as cyclohexane, hexane, etc.), which have problems such as flammability, toxicity and difficulty in waste liquid treatment.

[0008] Chinese patent application CN114853243A discloses a method for recovering tetrahydroimine from crystallization mother liquor through acidification, extraction, and resin adsorption. While this method achieves partial resource recovery, the process is complex, involving multiple acid-base adjustments and resin regeneration, resulting in high costs. Another Chinese patent application CN116444415A proposes a method for converting impurities and crystallizing them by treating the concentrate at high temperatures (155~165℃). However, this method requires high temperatures (>150℃) and long reaction times (2~3h), resulting in high energy consumption and demanding high pressure and temperature resistance requirements for the equipment.

[0009] Therefore, developing a simple, energy-efficient, non-volatile organic solvent-free method for purifying 1,2,3,6-tetrahydrophthalimide remains a pressing technical problem to be solved in this field.

[0010] Therefore, this invention is proposed to solve the above-mentioned technical problems. Summary of the Invention

[0011] This invention aims to provide a purification method for 1,2,3,6-tetrahydrophthalimide, addressing the problems of low product purity, organic solvent contamination, high energy consumption, or complex operation in existing technologies. This invention utilizes a deep eutectic solvent with a specific composition as the extraction medium and precisely controls the dissolution temperature and the proportion of water added as the antisolvent, achieving highly efficient and selective dissolution and crystallization of the target product in the crude product, thereby obtaining high-purity, high-yield 1,2,3,6-tetrahydrophthalimide.

[0012] To achieve the above objectives, the present invention provides a method for purifying 1,2,3,6-tetrahydrophthalimide, comprising the following steps:

[0013] S1. Preparation of deep eutectic solvent: Mix hydrogen bond acceptor and hydrogen bond donor, heat and stir until a clear and transparent liquid is obtained;

[0014] S2. Mix crude 1,2,3,6-tetrahydrophthalimide with the deep eutectic solvent prepared in S1, heat, stir until the crude product is completely dissolved, and cool to room temperature to obtain a solution.

[0015] S3. Add water to the solution, stir and mix, then let it stand to crystallize.

[0016] S4. Filtration: Collect the precipitated crystals and wash them with water. The filtrate is used to recover the deep eutectic solvent.

[0017] S5. Dry the washed crystals to obtain purified 1,2,3,6-tetrahydrophthalimide.

[0018] Furthermore, the hydrogen bond acceptor in S2 is one or more of choline chloride, betaine, and tetrabutylammonium chloride; the hydrogen bond donor is one or more of urea, thiourea, ethylene glycol, and glycerol.

[0019] Furthermore, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:2.

[0020] Furthermore, the heating temperature described in S1 is 70~80°C.

[0021] Furthermore, the mass ratio of the crude product to the deep eutectic solvent in S2 is 1:3 to 1:5.

[0022] Furthermore, the mass ratio of water to deep eutectic solvent in S3 is 1:2 to 1:4.

[0023] Furthermore, the method for recovering the deep eutectic solvent from the filtrate in step S4 is as follows: the filtrate is distilled under reduced pressure to recover the deep eutectic solvent, and the recovered deep eutectic solvent is recycled for step S2.

[0024] Furthermore, in S4, the mass ratio of washing water to crystals is 2:1 to 5:1, and the number of washing cycles is 1 to 3.

[0025] Furthermore, the drying described in S5 is vacuum drying, with a drying temperature of 50–70°C, a vacuum degree of -0.08–-0.1 MPa, and a drying time of 2–5 hours.

[0026] Furthermore, the crude 1,2,3,6-tetrahydrophthalimide is the filter residue obtained by direct distillation of the mother liquor obtained after crystallization filtration during the preparation of 1,2,3,6-tetrahydrophthalimide, followed by biochemical treatment of the distillate fraction.

[0027] The beneficial effects of this invention are:

[0028] This invention utilizes the differentiated solubility of deep eutectic solvents in 1,2,3,6-tetrahydrophthalimide and its impurities. Combined with precisely controlled dissolution temperature (130-140°C) and the ratio of antisolvent to water (1:2-1:4), the target product precipitates in high purity during cooling crystallization. Experiments have shown that the purity of the obtained product can reach over 98.5%, fully meeting the high standards required for pesticide synthesis. Furthermore, the deep eutectic solvent used is composed of inexpensive, non-toxic, and biodegradable components (such as choline chloride, urea, and ethylene glycol), without involving any volatile organic solvents. This avoids the use of flammable and toxic solvents such as cyclohexane and hexane in traditional extraction methods, significantly reducing the burden of wastewater treatment and making it environmentally friendly. In addition, compared to the high-temperature treatment of 155-165°C in existing technologies, the dissolution temperature of this invention is only 130-140°C, and the holding time is short, significantly reducing energy consumption.

[0029] In this invention, the deep eutectic solvent can be recovered from the filtrate through simple vacuum distillation, achieving a recovery rate of over 90%. The recovered solvent exhibits stable performance and can be recycled multiple times, further reducing production costs. This method is highly adaptable to raw materials, particularly suitable for recovering 1,2,3,6-tetrahydrophthalimide from the distillation residue of the crystallization mother liquor. Treating this residue as hazardous waste would be costly, but this invention transforms it into a valuable resource, additionally recovering 1,2,3,6-tetrahydrophthalimide, resulting in significant economic value. Furthermore, the entire process involves only conventional unit operations such as mixing, heating and dissolving, adding water for crystallization, and filtering and drying, requiring no complex equipment and facilitating industrial scale-up. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] In this embodiment, the content of 1,2,3,6-tetrahydrophthalimide crude product is 85%, and the amount of 1,2,3,6-tetrahydrophthalimide crude product used in S2 of this embodiment is 5 kg.

[0033] The example provides a method for purifying 1,2,3,6-tetrahydrophthalimide, specifically including the following steps:

[0034] S1. Preparation of deep eutectic solvent: Take choline chloride and urea in a molar ratio of 1:2, place them in a round-bottom flask, heat and stir in an 80°C water bath for 30 minutes until a clear and transparent liquid is formed. After cooling, the choline chloride-urea deep eutectic solvent is obtained and set aside.

[0035] S2. Dissolution: Add crude 1,2,3,6-tetrahydrophthalimide (crude product to solvent mass ratio 1:3) to the above deep eutectic solvent, heat to 135℃, stir for 15 minutes until the solid is completely dissolved, and obtain the solution. Then cool naturally to room temperature.

[0036] S3. Add deionized water to the solution, with a water-to-deep eutectic solvent mass ratio of 1:3. Stir and mix thoroughly, then let stand for 1 hour to allow crystallization. A large amount of white needle-like crystals will precipitate.

[0037] S4. Filter the crystals and collect them. Wash the crystals three times with deionized water, with the ratio of water volume to the wet weight of the crystals being 3:1 each time.

[0038] S5. Place the washed crystals in a vacuum drying oven at 50°C and a vacuum of -0.09 MPa for 3 hours to obtain 1,2,3,6-tetrahydrophthalimide.

[0039] The purity (HPLC) was 98.5%, and the recovery rate of 1,2,3,6-tetrahydrophthalimide in the crude product was 95.1%.

[0040] Example 2

[0041] In the example, the crude 1,2,3,6-tetrahydrophthalimide contained 90% 1,2,3,6-tetrahydrophthalimide, and the amount of crude 1,2,3,6-tetrahydrophthalimide used in Example S2 was 5 kg.

[0042] The example provides a method for purifying 1,2,3,6-tetrahydrophthalimide, specifically including the following steps:

[0043] S1. Preparation of deep eutectic solvent: Take choline chloride and urea in a molar ratio of 1:2, place them in a round-bottom flask, heat and stir in an 80°C water bath for 30 minutes until a clear and transparent liquid is formed. After cooling, the choline chloride-urea deep eutectic solvent is obtained and set aside.

[0044] S2. Dissolution: Add crude 1,2,3,6-tetrahydrophthalimide (crude product to solvent mass ratio 1:4) to the above deep eutectic solvent, heat to 130℃, stir for 20 minutes until the solid is completely dissolved, and obtain the solution. Then cool naturally to room temperature.

[0045] S3. Add deionized water to the solution, with a water-to-deep eutectic solvent mass ratio of 1:2. Stir and mix thoroughly, then let stand for 1 hour to allow crystallization. A large amount of white needle-like crystals will precipitate.

[0046] S4. Filter the crystals and collect them. Wash the crystals three times with deionized water, with the ratio of water volume to the wet weight of the crystals being 2:1 each time.

[0047] S5. Place the washed crystals in a vacuum drying oven at 50°C and a vacuum of -0.09 MPa for 3 hours to obtain 1,2,3,6-tetrahydrophthalimide.

[0048] The purity (HPLC) was 98.8%, and the recovery rate of 1,2,3,6-tetrahydrophthalimide in the crude product was 95.7%.

[0049] Example 3

[0050] In the example, the content of 1,2,3,6-tetrahydrophthalimide crude product was 95%, and the amount of 1,2,3,6-tetrahydrophthalimide crude product used in this example S2 was 5 kg.

[0051] The example provides a method for purifying 1,2,3,6-tetrahydrophthalimide, specifically including the following steps:

[0052] S1. Preparation of deep eutectic solvent: Take choline chloride and urea in a molar ratio of 1:2, place them in a round-bottom flask, heat and stir in an 80°C water bath for 30 minutes until a clear and transparent liquid is formed. After cooling, the choline chloride-urea deep eutectic solvent is obtained and set aside.

[0053] S2. Dissolution: Add crude 1,2,3,6-tetrahydrophthalimide (crude product to solvent mass ratio 1:5) to the above deep eutectic solvent, heat to 140℃, stir for 20 minutes until the solid is completely dissolved, and obtain the solution. Then cool naturally to room temperature.

[0054] S3. Add deionized water to the solution, with a water-to-deep eutectic solvent mass ratio of 1:4. Stir and mix thoroughly, then let stand for 1 hour to allow crystallization. A large amount of white needle-like crystals will precipitate.

[0055] S4. Filter the crystals and collect them. Wash the crystals once with deionized water, with the ratio of water volume to the wet weight of the crystals being 5:1 each time.

[0056] S5. Place the washed crystals in a vacuum drying oven at 50°C and a vacuum of -0.09 MPa for 3 hours to obtain 1,2,3,6-tetrahydrophthalimide.

[0057] The purity (HPLC) was 98.2%, and the recovery rate of 1,2,3,6-tetrahydrophthalimide in the crude product was 94.7%.

[0058] The filtrate obtained from step S4 of Examples 1-3 can be recycled after vacuum distillation to recover the deep eutectic solvent.

[0059] Comparative Example 1

[0060] In this embodiment, the content of 1,2,3,6-tetrahydrophthalimide crude product is 85%, and the amount of 1,2,3,6-tetrahydrophthalimide crude product used in S2 of this embodiment is 5 kg.

[0061] The example provides a method for purifying 1,2,3,6-tetrahydrophthalimide, specifically including the following steps:

[0062] S1. Preparation of deep eutectic solvent: Take choline chloride and urea in a molar ratio of 1:2, place them in a round-bottom flask, heat and stir in an 80°C water bath for 30 minutes until a clear and transparent liquid is formed. After cooling, the choline chloride-urea deep eutectic solvent is obtained and set aside.

[0063] S2. Dissolution: Add crude 1,2,3,6-tetrahydrophthalimide (crude product to solvent mass ratio 1:3) to the above deep eutectic solvent, heat to 125℃, stir for 15 minutes until the solid is completely dissolved, and obtain the solution. Then cool naturally to room temperature.

[0064] S3. Add deionized water to the solution, with a water-to-deep eutectic solvent volume ratio of 1:3. Stir and mix thoroughly, then let stand for 1 hour to allow crystallization. A large number of white needle-like crystals will precipitate.

[0065] S4. Filter the crystals and collect them. Wash the crystals three times with deionized water, with the ratio of water volume to the wet weight of the crystals being 3:1 each time.

[0066] S5. Place the washed crystals in a vacuum drying oven at 50°C and a vacuum of -0.09 MPa for 3 hours to obtain 1,2,3,6-tetrahydrophthalimide.

[0067] The content (HPLC) was 90.5%, and the recovery rate of 1,2,3,6-tetrahydrophthalimide in the crude product was 85.1%.

[0068] Comparative Example 2

[0069] In this embodiment, the content of 1,2,3,6-tetrahydrophthalimide crude product is 85%, and the amount of 1,2,3,6-tetrahydrophthalimide crude product used in S2 of this embodiment is 5 kg.

[0070] The example provides a method for purifying 1,2,3,6-tetrahydrophthalimide, specifically including the following steps:

[0071] S1. Preparation of deep eutectic solvent: Take choline chloride and urea in a molar ratio of 1:2, place them in a round-bottom flask, heat and stir in an 80°C water bath for 30 minutes until a clear and transparent liquid is formed. After cooling, the choline chloride-urea deep eutectic solvent is obtained and set aside.

[0072] S2. Dissolution: Add crude 1,2,3,6-tetrahydrophthalimide (crude product to solvent mass ratio 1:3) to the above deep eutectic solvent, heat to 160℃, stir for 15 minutes until the solid is completely dissolved, and obtain the solution. Then cool naturally to room temperature.

[0073] S3. Add deionized water to the solution, with a water-to-deep eutectic solvent volume ratio of 1:3. Stir and mix thoroughly, then let stand for 1 hour to allow crystallization. A large number of white needle-like crystals will precipitate.

[0074] S4. Filter the crystals and collect them. Wash the crystals three times with deionized water, with the ratio of water volume to the wet weight of the crystals being 3:1 each time.

[0075] S5. Place the washed crystals in a vacuum drying oven at 50°C and a vacuum of -0.09 MPa for 3 hours to obtain 1,2,3,6-tetrahydrophthalimide.

[0076] The content (HPLC) was 91.5%, and the recovery rate of 1,2,3,6-tetrahydrophthalimide in the crude product was 82.6%.

[0077] Comparative Example 3

[0078] In this embodiment, the content of 1,2,3,6-tetrahydrophthalimide crude product is 85%, and the amount of 1,2,3,6-tetrahydrophthalimide crude product used in S2 of this embodiment is 5 kg.

[0079] The example provides a method for purifying 1,2,3,6-tetrahydrophthalimide, specifically including the following steps:

[0080] S1. Preparation of deep eutectic solvent: Take choline chloride and urea in a molar ratio of 1:2, place them in a round-bottom flask, heat and stir in an 80°C water bath for 30 minutes until a clear and transparent liquid is formed. After cooling, the choline chloride-urea deep eutectic solvent is obtained and set aside.

[0081] S2. Dissolution: Add crude 1,2,3,6-tetrahydrophthalimide (crude product to solvent mass ratio 1:3) to the above deep eutectic solvent, heat to 125℃, stir for 15 minutes until the solid is completely dissolved, and obtain the solution. Then cool naturally to room temperature.

[0082] S3. Add deionized water to the solution, with a water-to-deep eutectic solvent volume ratio of 1:6. Stir and mix thoroughly, then let stand for 1 hour to allow crystallization. A large number of white needle-like crystals will precipitate.

[0083] S4. Filter the crystals and collect them. Wash the crystals three times with deionized water, with the ratio of water volume to the wet weight of the crystals being 3:1 each time.

[0084] S5. Place the washed crystals in a vacuum drying oven at 50°C and a vacuum of -0.09 MPa for 3 hours to obtain 1,2,3,6-tetrahydrophthalimide.

[0085] The content (HPLC) was 93.5%, and the recovery rate of 1,2,3,6-tetrahydrophthalimide in the crude product was 88.1%.

[0086] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for purifying 1,2,3,6-tetrahydrophthalimide, characterized in that, Includes the following steps: S1. Preparation of deep eutectic solvent: Mix hydrogen bond acceptor and hydrogen bond donor, heat and stir until a clear and transparent liquid is obtained; S2. Mix crude 1,2,3,6-tetrahydrophthalimide with the deep eutectic solvent prepared in S1, heat, stir until the crude product is completely dissolved, and cool to room temperature to obtain a solution. S3. Add water to the solution, stir and mix, then let it stand to crystallize. S4. Filtration: Collect the precipitated crystals and wash them with water. The filtrate is used to recover the deep eutectic solvent. S5. Dry the washed crystals to obtain purified 1,2,3,6-tetrahydrophthalimide.

2. The purification method according to claim 1, characterized in that, The hydrogen bond acceptor in S2 is one or more of choline chloride, betaine, and tetrabutylammonium chloride, and the hydrogen bond donor is one or more of urea, thiourea, ethylene glycol, and glycerol.

3. The purification method according to claim 1, characterized in that, The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor in S2 is 1:

2.

4. The purification method according to claim 1, characterized in that, The heating temperature described in S1 is 70~80℃.

5. The purification method according to claim 1, characterized in that, The mass ratio of the crude product to the deep eutectic solvent in S2 is 1:3 to 1:5, and the heating temperature is 130 to 140°C.

6. The purification method according to claim 1, characterized in that, The mass ratio of water to deep eutectic solvent in S3 is 1:2 to 1:

4.

7. The purification method according to claim 1, characterized in that, The method for recovering the deep eutectic solvent from the filtrate described in S4 is as follows: the deep eutectic solvent is recovered from the filtrate under reduced pressure distillation, and the recovered deep eutectic solvent is recycled for step S2.

8. The purification method according to claim 1, characterized in that, The mass ratio of washing water to crystals in S4 is 2:1 to 5:1, and the number of washing cycles is 1 to 3.

9. The purification method according to claim 1, characterized in that, The drying described in S5 is vacuum drying, with a drying temperature of 50-70℃, a vacuum degree of -0.08--0.1MPa, and a drying time of 2-5h.

10. The purification method according to claim 1, characterized in that, The crude 1,2,3,6-tetrahydrophthalimide is obtained by direct distillation of the mother liquor obtained after crystallization filtration during the preparation of 1,2,3,6-tetrahydrophthalimide, and the filter residue obtained by biochemical treatment of the distillate fraction.